Dear visitor, welcome to SPRINKLER TALK FORUM - You Got Questions, We've Got Answers. If this is your first visit here, please read the Help. It explains how this page works. You must be registered before you can use all the page's features. Please use the registration form, to register here or read more information about the registration process. If you are already registered, please login here.

The pressure is set that high on the reg. Our normal pressure at the meter is somewhere between 125# - 150#. I don't have a hosebibb between the meter & reg., so I'm going by memory of when we did the fresh install several years ago. The water coming to the house with the 18 weathermatics is now set to 100PSI(measured at the highest point next to a set of the valves). That's what we decided on, as I recall, to run the circuits for best coverage. I believe my irrigation guy had faith that the parts of the circuits could handle that pressure. It's a hilly, rural agricultural area and the high pressure is the norm for our elevation. I can try a reduction down to 80PSI, or so, and see what that does to the irrigation patterns. They're mostly all rotor circuits. I'm still uncomfortable with the 12000s, even doing that. At what pressure point could I be guaranteed they won't do their flex & spit trick??

Without knowing your exact system layout, it's difficult to answer where the regulator should be set. The system I know of is running 80 psi static and has the same issue. I would try cranking the regulator down to 70psi and see how things look. Another note...100psi at the highest point is the lowest the pressure will be. Valves at the lowest elevations will exceed the 100psi.
I'd be curious to know what kind of flow these zones require, and what size pipe the installer used.

with a mainline over 400 feet long, you are getting serious water hammer when the valves shut off (water hammer force is a function of the length of the upstream plumbing, and the velocity of the flow)

there is probably nothing you can do with pressure regulation alone that will stop the valves 'burping' water, so it is all on the master valve and the controller

CI. The flow rate measured on one of, what appears to be, the higher flowing circuits is 12.16 GPM and the feed pipe size from the valve is 1"(The valves are 1" valves). The lowest valve is about5 15-20 feet below the highest.

Wet_Boots. Thanks. I hadn't realized the amount of hammer was a function of the length of upstream & flow, but it makes perfect sense. The pressure reg is about 400' upstream, but there is no backflow device(it's an ag line that doesn't require one), so am wondering if the length to consider for upstream plumbing extends beyond the PR & meter, or does the PR regulate the flow for the purpose of reducing hammering?

I'm going to take your flow numbers with a grain of salt... That would total about 4 rotors per zone with a pressure of about 60 static. Based on static pressure of above 100psi, you're probably flowing closer to 15-16gpm if you indeed have 4 rotors per zone. Either way, turning down your pressure regulator to 70psi would give a dynamic pressure at the valve of close to 50psi. Now, subtract 5psi for the valve and laterals, and you're left with 45 psi at the heads. 45psi at the head is damn good! Not much difference in the radius of a rotor from 45-90psi. Unless of course you're using some commercial/golf course style heads. Of course, I'm basing all this off of poly pipe. If the pipe is PVC, then you'll probably have higher psi at the heads.
Water hammer is a product of excessive water flow through a given diameter of pipe. Length of the pipe is not a variable. 15gpm is about maximum for a 1" poly line. 20gpm for a 1" PVC line.
By turning down your regulator, you will also reduce your available flow at the end of the 400' mainline due to the friction loss of the water travelling through your 400' main line. But this also means that you will not exceed the maximum velocities for the 1" line which would cause any damaging water hammer.

OK, I've got a pretty big problem with the pressure. Couldn't find the meter I used to measure 100PSI and found my spare. It read 128PSI.. Yikes! Picked up a couple more at different stores today as a check. All are made in China..
Bottom line is all read 128 PSI.. OK, played with the pressure reg and no difference. It appears to have regulated it's last... Sooo, I need to rent a trencher and cut accross the 30' wide area that the feed pipe is buried in (somewhere). Until I do that and find the pipe(This should be less than 100' away from the controller) and get a new pressure reg and master valve installed at that point, I'm wasting everyone's time. So, I'll sign off for now and get things under control before asking again for help.

CI, I did measure the flow for a circuit having 4 Hunter PGP pop up rotors with blue nozzles and came up with 12.6GPM. I ran them today & checked the pressure while running, there was over 40 PSI still at the hose bibb.

An update:
I installed a new Pressure reg. and dropped the pressure down to 75-80psi(depending on valve elevation). My
installer put in a master valve and avoided most all the trenching I thought would be needed. Seems he'd included 3 extra wires from the controller to a valve box installed 4 years ago that was about 30 easy digging feet away from the incoming water line. He used 2 of the wires for the master valve. Additionally he was easily able to find the water line with a water probe.

Things are looking up, the valves are no longer burping when shut off. I'll go through them at my leisure and
do a thorough cleaning.
-MC